Waterproof cases are fine; lockers exist but cost.

Yes, you can bring a phone or camera in a waterproof case, and most places have lockers for rent.

The key question is whether you actually need your phone with you. If you’re just there to swim, use the locker. It’ll cost you maybe $5–$10 and keep everything dry and safe. Waterproof cases are great until they aren’t—a tiny bit of sand or a weak seam can turn your phone into a paperweight in seconds.

If you do bring a case, test it first. Put a paper towel inside, submerge it in a sink, and see if it stays dry. Don’t learn about a leak while standing in a wave pool.

Also check the venue’s specific rules. Some water parks ban cameras for privacy reasons, even in cases. Lockers don’t have that problem.

Just test your case first before trusting it with your phone. Future You will appreciate not having to explain how the phone ended up at the bottom of the lazy river.